feat(buffers): add buffers_sort option (#2793)

* refactor: add sort_buffers option to buffers picker

* refactor: validate sort_buffers opt is a function

lua/telescope/builtin/__internal.lua

@@ -912,6 +912,10 @@ internal.buffers = function(opts)
     end)
   end
 
+  if type(opts.sort_buffers) == "function" then
+    table.sort(bufnrs, opts.sort_buffers)
+  end
+
   local buffers = {}
   local default_selection_idx = 1
   for _, bufnr in ipairs(bufnrs) do